Drinking massive amounts of water is a good way to defeat a drug test. However, it is fairly easy to tell when someone has been flushing by testing the levels of Creatine in the urine, which for most people are in a fairly tight range most of the time. Creatine can be bought as a supplement at places like GNC, etc. because bodybuilders and athletes like to use it to stimulate muscle growth. Using the correct amount of vitamin (b-complex for color) and creatine (for counter-deviousness) supplements, one could theoretically fool the test.